In an effort to reduce emissions and to comply with more strict clean air standards, manufacturers of various diesel engine components have begun exploring an alternative engine strategy commonly referred to as homogeneous charge compression ignition (HCCI). An HCCI injection differs from a traditional diesel injection in that an HCCI injection introduces fuel into the engine cylinder near bottom dead center of the compression stroke as opposed to near top dead center, as in conventional diesel operation. This operational adjustment allows the diesel fuel and air to become a relatively lean, homogeneous mixture unlike a traditional injection system. Scientific research has found that the resulting homogeneous mixture burns more cleanly and efficiently. At the same time, engineers discovered that an HCCI injection lost its efficiency advantages as the engine was operated under larger load conditions, and the traditional injection strategy appeared preferable under such large load circumstances.
Based on the engineering and scientific research, previous art in HCCI research taught using two separate fuel injectors, one for traditional diesel ignition under high load conditions, and one for HCCI injection under lower load conditions. While two fuel injectors can enable dual modes of operation, it can be appreciated that a single fuel injector capable of both HCCI and traditional injection would be advantageous because it would have less components prone to failure or malfunction. Therefore, a need was created for a fuel injector that would facilitate the fuel spray into the engine cylinder under both traditional and HCCI fuel injection operations.
One known strategy for having a dual mode fuel injector is achieved with a nested needle arrangement or a dual concentric needle arrangement. A nested needle arrangement has proven problematic because engineers have found that boring a hole with the necessary length and diameter, as well as grinding the corresponding valve seat deep inside the bore was difficult to impossible to accomplish with conventional machining techniques.
Previous art in the area is described in U.S. Pat. No. 4,856,713, which issued to Burnett on Aug. 15, 1989 and is entitled Dual Fuel Injector. This patent teaches a fuel injector that is capable of injecting both liquid and slurry fuels. To accomplish this task, two defined sets of openings were manufactured into the fuel injector, one for the liquid fuel and one for the slurry fuel. The two definite openings were accomplished by threadably coupling a replaceable tip to the outlet end of the nozzle valve structure. The replaceable tip contained an outlet, an outer valve surface and an inner valve seat. Burnett taught that threading of the replaceable tip with the valve structure is utilized for easy removal and replacement of tip section.
The injector taught by Burnett is not useful in diesel engines running under high pressure and requiring well-filtered diesel fuel. Threading, by its nature, cannot reliably produce a proper centerline alignment needed for this type of fuel injector having very tight diametrical clearances between its moving parts. Threading is not a permanent binding method; threading of mating sections requires tiny openings and irregularities so the two sections can be attached and unattached without much difficulty. Furthermore, a dual fuel injector of this type must be centered along a central axis; any disruption in the concentricity could cause a malfunction of the fuel injection process, such as a jammed or stuck needle. Once again, a threaded model, by its nature, cannot assure that the needle valve would be concentric. Therefore, the teaching of threading and removability is not helpful for the type of dual fuel injectors necessary for distillate diesel fuel injection systems.
The present invention is directed to overcoming one or more of the problems set forth above.